<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <h1 id="h">
        <p>123</p>
    </h1>
    <h1 class="a1">
        <p>1</p>
    </h1>
    <h1 class="a1">
        <p>2</p>
    </h1>
    <h1 class="a1">
        <p>3</p>
    </h1>
    <button onclick="a()">点我变456</button>
    <button onclick="b()">点我变123</button>
    <input type="text" onkeydown="key()"></input>
</body>

</html>

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